Newton’s First Law of Motion *

Newton’s First Law An object at rest tends to stay at rest and an object in motion tends to stay in motion unless acted upon by an unbalanced force.

What does this mean? Basically, an object will “keep doing what it was doing” unless acted on by an unbalanced force. If the object was sitting still, it will remain stationary. If it was moving at a constant velocity, it will keep moving. It takes force to change the motion of an object.

What is meant by unbalanced force? If the forces on an object are equal and opposite, they are said to be balanced, and the object experiences no change in motion. If they are not equal and opposite, then the forces are unbalanced and the motion of the object changes.

1st Law Unless acted upon by an unbalanced force, this golf ball would sit on the tee forever.

FORCES Forces in Combination Predict how the box will move based on the forces applied to it. 50N 250N 200N

FORCES Forces in Combination Predict how each box will move based on the forces applied to it. 50N 40N 40N 30N 40N 50N 40N 40N 50N 50N

Determine the net force in each example. FORCES Forces in Combination Determine the net force in each example. 23N to the right 29N to the left 30N to the right 15N to the left

Check Yourself ? * Physics 1 (Garcia) SJSU

It’s a force we sometimes cannot see – friction. Why then, do we observe every day objects in motion slowing down and becoming motionless seemingly without an outside force? It’s a force we sometimes cannot see – friction.

Newton’s First Law is also called the Law of Inertia Inertia: the tendency of an object to resist changes in its state of motion The First Law states that all objects have inertia. The more mass an object has, the more inertia it has (and the harder it is to change its motion).

In outer space, away from gravity and any sources of friction, a rocket ship launched with a certain speed and direction would keep going in that same direction and at that same speed forever. Voyager 1 is a space probe launched by NASA on September 5, 1977. The probe has left the solar system 20,638,006,500. KM. The robotic spacecraft is streaking at 35,000 mph toward an encounter with a star called Proxima Centauri, which lies 17.6 light-years from Earth. It will get there in 40,000 years.

Newtons’s 1st Law and You Don’t let this be you. Wear seat belts. Because of inertia, objects (including you) resist changes in their motion. When the car going 80 km/hour is stopped by the brick wall, your body keeps moving at 80 m/hour.

Newton’s Laws Critical Thinking A passenger sitting in the rear of a bus claims that she was injured as the driver slammed on the brakes causing a suitcase to come flying toward her from the front of the bus. If you were the judge in this case, what decision would you make?

Demo: Riding Light Rail When a moving train stops, you continue moving forward. When the stopped train starts moving again, you remain stationary and are thrown backwards * Physics 1 (Garcia) SJSU

Demo: Rolling, rolling, rolling All moving together WALL Bottom car stops. Other two continue With same speed. * Physics 1 (Garcia) SJSU

Demo: Tablecloth Pull Flower Vase Tablecloth Yank quickly * Physics 1 (Garcia) SJSU

Demo: Ring Yank Ring Beaker Coin Yank quickly * Physics 1 (Garcia) SJSU